1. Field of the Invention
The present invention relates to methods for producing a multilayer printed wiring board.
2. Discussion of the Background
Multilayer printed wiring boards widely used for various electronic instruments are required to have thin layer and ultrafine wiring circuit to achieve downsizing and high-functionalization of electronic instruments. As a technique for producing a multilayer printed wiring board, a production method using a build-up process of alternately layering an insulating layer and a conductive layer on a core substrate is known. For example, a curable resin composition is laminated on an internal-layer circuit substrate with an adhesive film, and the curable resin composition is cured to form an insulating layer. Thereafter, the insulating layer is roughened with an oxidizing agent such as alkaline potassium permanganate solution and the like, a plating seed layer is formed on the roughened surface by electroless plating according to a semi-additive process, and then a conductive layer is formed by electroplating. In conductive layer formation by a semi-additive process here, the surface of an insulating layer needs to be roughened with an oxidizing agent (concaves and convexes are formed on the surface) as mentioned above to provide an anchor effect between conductive layers, so that a conductive layer having high adhesion strength can be obtained. When a plating seed layer, which is unnecessary for circuit formation, is removed by etching, however, problems occur in that the seed layer in the anchor part is difficult to remove, and when the seed layer in the anchor part is etched under conditions permitting sufficient removal, the wiring pattern is remarkably dissolved, thus preventing ultrafine wiring.
To solve such problems, a method including transferring a metal film layer to be a plating seed layer onto an adherend by a film with a metal film has been tried. For example, JP-A-2004-230729 and JP-A-2002-324969 patent disclose a method of forming a conductive layer, which includes preparing a film with a metal film, wherein a metal film layer is formed on a support layer, via a release layer by vapor deposition and the like, transferring the metal film layer of the film with the metal film onto the surface of an insulating layer or prepreg, which is on the substrate, and forming a conductive layer on the transferred metal film layer by plating and the like. In the method of JP-A-2004-230729, a film with a metal film using fluorocarbon resin, polyolefin resin, polyvinyl alcohol resin as a release layer is used, and in the method of JP-A-2002-324969, a film with a metal film using an adhesive containing an adhesive resin such as acrylic resin, melamine resin and the like as a release layer is used. On the other hand, JP-A-9-296156 discloses an adhesive film obtained by directly forming a metal film layer on a support layer by vapor deposition and the like and forming a resin composition layer thereon.